Ship bottoms, buoys, fishing nets, and other structures submerged in seawater such as marine antifouling sheets and cooling water intake or discharge pipes are infested with organisms such as barnacles, tube worms and algae that attach to the surface of these structures and cause various troubles. It is routine practice to prevent the attachment of these marine fouling organisms by coating the surfaces of the aforementioned items with antifouling paints.
Organotins, and in particular tributyltins, have been the premier method of providing marine antifouling performance to organic paints. With the recent restrictions on the use of these toxic coatings in many countries, the boat and ship owners have fallen back to the technically inferior but less toxic copper oxide based coatings. The life of copper oxide based coatings rarely exceed 2 years in normal fouling conditions while the self-polishing tributyltinmethacrylate copolymers often exceeded 5 years. Also, coatings prepared from tributyltins can be pigmented in bright colors which had appeal for many boat and ship owners. Therefore, a dissatisfaction existed wherever the organotins were banned because copper oxide based coatings did not satisfy the needs of the boat and ship owners and operators.
Fouling control coatings based on silicone elastomers, such as polydimethylsiloxanes, have been known since the early 1970's. For instance, silicone-based formulations are disclosed in U.S. Pat. Nos. 4,025,693; 4,080,190; 4,227,929; and others. Also, Japanese patent application 96830/76 discloses an antifouling paint that uses a mixture of a silicone oil and an oligomer-like silicone rubber having terminal hydroxyl groups.
Silicones are based on polymers comprised of a backbone of silicon-oxygen-silicon atoms linked together. They are thus different chemically from organic materials which are mostly based on polymers composed of a backbone of carbon-to-carbon atoms linked together. It is this difference --the silicon-oxygen linkage--which accounts for the unique properties of silicones. The silicone bond linkage is similar to bond linkage found in other high temperature resistant materials such as quartz, glass and sand; hence the outstanding high temperature properties of room temperature vulcanizing (RTV) silicone rubber. This chemical makeup also accounts for the general inertness of RTV silicone rubber toward many deteriorating influences such as ozone, chemicals, weathering and radiation.